Gradient, and How the Multipliers Stack

First, gradient. Descending lengthens your stop through two mechanisms:

1. Gravity joins the wrong team. On a descent, part of the vehicle's weight actively pushes it forward — your brakes must cancel that on top of the kinetic energy. Same speed, same surface, longer stop; steeper grade, worse.
2. Heat arrives sooner. Sustained descent braking cooks the brakes toward fade, degrading them exactly when the gradient is demanding more of them. This is why engine braking on a long descent isn't just advice — it's the mechanism that keeps your braking budget intact for the moment you need it.

Now the sobering part: these factors don't take turns.

Scenario — night, steady rain, a car on tyres near the legal minimum, 80 km/h on a rural highway:

• Baseline 80 km/h dry: about 65 m
• Steady rain (×2 braking): about 97 m total
• Worn-legal tread pushing wet grip toward f 0.3: total toward ~120 m
• Night: your headlights define how far ahead you detect the hazard at all — so a chunk of that 120 m may be spent before detection even starts the clock.

No single factor was extreme. The stack is. And every element was visible before the journey began — the forecast, the tread, the clock. That's the lesson's real point: stopping distance is mostly decided before the hazard appears — in your speed choice, your tyre maintenance, and the honesty to re-price your numbers when conditions move. The hazard only grades the paper.